/Engine/Plugins/Online/OnlineSubsystemUtils/Source/OnlineSubsystemUtils/Public/PartyBeaconState.h
Updates the platform on an existing reservation (Used when MMS does not set a platform when handing out a match assignment)
true if a reservation exists, false otherwise
virtual bool UpdateMemberPlatform ( const [FUniqueNetIdRepl](API\Runtime\Engine\GameFramework\FUniqueNetIdRepl) & PartyMember, const [FString](API\Runtime\Core\Containers\FString) & PlatformName )